The invention relates to solid particulate filter bodies and other selectively plugged honeycomb structures and, in particular, to methods and related apparatus for fabricating such structures.
It is well known that a solid particulate filter body may be fabricated from a cellular or honeycomb structure which typically consists of a multiplicity of mutually adjoining and substantially parallel hollow passages or cells extending through the structure and through and between a pair of its opposing end faces where the open, transverse cross-sections of the cells are exposed. The cells themselves are formed by thin, porous walls which extend continuously between the end faces and intersect with one another so as to form a continuous matrix across the end faces. The cells are typically provided in densities ranging from one-tenth to more than one hundred cells per square centimeter. To fabricate such filter bodies, one end of all of the cells are typically blocked by manifolding (i.e. plugging), sealing or otherwise, a first subset of cells being blocked at one end face and the remaining cells being blocked at the remaining end face of a honeycomb structure. Either of the end faces may then be used as the inlet face of the resulting filter. The contaminated fluid is brought under pressure to the inlet face and enters the filter body via those cells which are open at that face (i.e. the "inlet" cells). Because these cells are blocked at the opposing "outlet" end face, the contaminated fluid is forced through the thin, porous walls into adjoining cells which are desirably sealed at the inlet face and open at the outlet face (i.e. "outlet" cells). The solid particulate contaminant in the fluid which is too large to pass through the porous openings in the thin walls is left behind and a cleansed fluid exits the filter through the outlet face for use.
For the mass production of such filters, it is highly desirable to be able to seal selected cell ends as rapidly and as inexpensively as possible. Thousands of cells may be provided in each honeycomb structure, all or substantially all of which must be sealed at one or the other end face. Rodney Frost and Irwin Lachman describe in a pending application Ser. No. 165,646, filed July 3, 1980, entitled FILTER AND RELATED APPARATUS, and assigned to the assignee of this application, a solid particulate filter body typically formed from an extruded ceramic-based substrate in which alternate cells at either end face are sealed in a checkered or checkerboard pattern such that each inlet cell shares thin, common walls with only outlet cells and each outlet cell shares thin, common walls with only inlet cells. These filter bodies are described as being fabricated by plugging the individual cell ends with a hand-held, single nozzle, air actuated sealant gun. Manifolding individual cells by this process is long and tedious and is not suited for the commercial production of such filters which may have thousands of cells to be plugged. Frost and Lachman also postulate the use of a sealant gun having an array of nozzles so that the plugging mixture may be simultaneously injected into a subset or all of the selected cells at each end face of the structure.
In a related area, U.S. Pat. No. 4,410,591 describes fabricating a multiple flow path filter body from a honeycomb structure having its cells arranged in adjoining columns. All of the cell ends at an end face of a honeycomb structure are filled with a temporary resist material such as a meltable plastic. The resist material is removed from selected columns of cells by cutting it away together with the intervening cell walls along the column at the end face. The cut at the end face is covered with a permanent sealant thereby creating a channel along each selected column which is transverse to the end face. The remaining temporary resist material is removed by suitable means. Alternatively, the selected columns are first cut away and then the resist material is applied and blown from the selected columns by compressed air directed down the cuts. Although these methods could be adapted to fabricate a type of filter body by applying sufficient sealant to plug the cells ends exposed by the cuts, it would be unsuited for plugging patterns other than columns and could not, for example, be used to produce the checked pattern of plugged cell ends described in the aforesaid application Ser. No. 165,646. Moreover, it would be desirable to eliminate the use of the temporary resist material as this adds an additional step and expense to the process.